Commit 500f8f9b authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Thomas Gleixner
Browse files

tick: Assume timekeeping is correctly handed over upon last offline idle call 



The timekeeping duty is handed over from the outgoing CPU on stop
machine, then the oneshot tick is stopped right after.  Therefore it's
guaranteed that the current CPU isn't the timekeeper upon its last call
to idle.

Besides, calling tick_nohz_idle_stop_tick() while the dying CPU goes
into idle suggests that the tick is going to be stopped while it is
actually stopped already from the appropriate CPU hotplug state.

Remove the confusing call and the obsolete case handling and convert it
to a sanity check that verifies the above assumption.

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-16-frederic@kernel.org
parent 3f69d04e

include/linux/tick.h

+2 −0
Original line number Diff line number Diff line
@@ -29,8 +29,10 @@ static inline void tick_cleanup_dead_cpu(int cpu) { } 


#if defined(CONFIG_GENERIC_CLOCKEVENTS) && defined(CONFIG_HOTPLUG_CPU)

extern int tick_cpu_dying(unsigned int cpu);

extern void tick_assert_timekeeping_handover(void);

#else

#define tick_cpu_dying	NULL

static inline void tick_assert_timekeeping_handover(void) { }

#endif



#if defined(CONFIG_GENERIC_CLOCKEVENTS) && defined(CONFIG_SUSPEND)

kernel/cpu.c

+1 −0
Original line number Diff line number Diff line
@@ -1399,6 +1399,7 @@ void cpuhp_report_idle_dead(void) 
	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);



	BUG_ON(st->state != CPUHP_AP_OFFLINE);

	tick_assert_timekeeping_handover();

	rcutree_report_cpu_dead();

	st->state = CPUHP_AP_IDLE_DEAD;

	/*

kernel/sched/idle.c

+0 −1
Original line number Diff line number Diff line
@@ -291,7 +291,6 @@ static void do_idle(void) 
		local_irq_disable();



		if (cpu_is_offline(cpu)) {

			tick_nohz_idle_stop_tick();

			cpuhp_report_idle_dead();

			arch_cpu_idle_dead();

		}

kernel/time/tick-common.c

+4 −0
Original line number Diff line number Diff line
@@ -396,6 +396,10 @@ int tick_broadcast_oneshot_control(enum tick_broadcast_state state) 
EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);



#ifdef CONFIG_HOTPLUG_CPU

void tick_assert_timekeeping_handover(void)

{

	WARN_ON_ONCE(tick_do_timer_cpu == smp_processor_id());

}

/*

 * Stop the tick and transfer the timekeeping job away from a dying cpu.

 */

kernel/time/tick-sched.c

+1 −12
Original line number Diff line number Diff line
@@ -1160,18 +1160,7 @@ static bool report_idle_softirq(void) 


static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)

{

	/*

	 * If this CPU is offline and it is the one which updates

	 * jiffies, then give up the assignment and let it be taken by

	 * the CPU which runs the tick timer next. If we don't drop

	 * this here, the jiffies might be stale and do_timer() never

	 * gets invoked.

	 */

	if (unlikely(!cpu_online(cpu))) {

		if (cpu == tick_do_timer_cpu)

			tick_do_timer_cpu = TICK_DO_TIMER_NONE;

		return false;

	}

	WARN_ON_ONCE(cpu_is_offline(cpu));



	if (unlikely(!tick_sched_flag_test(ts, TS_FLAG_NOHZ)))

		return false;